Java Persistence API (JPA) is a Java specification for object-relational mapping (ORM). It provides a convenient way to interact with databases using Java objects, making database operations more intuitive and less error-prone. One of the central components in JPA is the EntityManager. In this blog, we will delve into the EntityManager, understanding its role, lifecycle, and usage in JPA.
What is EntityManager?
The EntityManager is a fundamental part of JPA. It acts as a bridge between your application and the underlying database, allowing you to perform various database operations, such as inserting, updating, and querying data, using Java objects and object-oriented concepts.
Operations of Entity Manager
The EntityManager has a well-defined lifecycle that mirrors the lifecycle of your application. Here are the main stages of its lifecycle:
Creating Entity Manager–
You create an EntityManager when you need to interact with the database. You typically obtain an EntityManager from an EntityManagerFactory, which manages the EntityManager instances.
EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory(“your-persistence-unit”);
EntityManager entityManager = entityManagerFactory.createEntityManager();
During this phase, the EntityManager is active and associated with a particular persistence context. In this state, the EntityManager tracks changes made to entities and can persist these changes to the database.
: The persistence context is a temporary workspace that holds managed entities and their changes. When an entity is managed, any changes made to it are automatically synchronized with the database when a transaction is committed.
The EntityManager works within a transaction context. Transactions ensure data consistency and integrity. You can start and commit transactions explicitly, or JPA can manage them for you.
EntityTransaction transaction = entityManager.getTransaction();
// Perform database operations
Detaching Entities: You can detach an entity from the EntityManager, effectively taking it out of the managed state. Detached entities are no longer synchronized with the database.
Closing: When you are done with an EntityManager, you should close it to release resources and ensure that no further operations can be performed.